Valves are used in a variety of applications, from large-scaled, bulk flow applications to relatively small flow rate applications. More recently, valves have been used in implantable devices for infusion drug treatment. Flow rates for this application usually range from tenths of milliliters per day to a few milliliters per hour.
Typical valves have a default position. The position may fail opened or closed in the event that energy or an actuation force is lost. In a typical fail-closed valve, a pneumatic or electric force is applied to open the valve and keep it open. For example, in a typical solenoid valve that fails closed, a current is applied to a coil, inducing a magnetic force that drives a piston against a spring, opening the valve. To keep the valve open, the current is continuously applied, consuming energy.
In implantable devices, the available energy is limited by the power source. In some cases, the implanted devices may be recharged through radio frequency energy collection. However, the system is still limited by the size of the battery and the frequency of available recharging. As such, a valve that requires continuous power to maintain a desired position draws down the available power, usually requiring more frequent recharging or battery replacement.
In addition, the continuous use of energy to maintain valve position may cause other problems. Continuous use of sensitive circuitry may cause thermal strain. In various actuation systems, continuous use may lead to leaks, stress on parts, and undesired chemical reactions that adversely affect performance of the valve.
As such, typical valve systems and methods for use may suffer from deficiencies in energy use and use-induced stresses. Many other problems and disadvantages of prior solutions will become apparent to one skilled in the art after comparing such prior solutions with the present invention as described herein.